"Cannot Modify Sprite" Notice Prevents Doing Anything

The Cannot Modify Sprite notice prevents me from saving, adding layers, opening new canvases, exiting the program, and every other option. I’m not sure how it started.

I was having the same issue just now but used a random trick I learned for when Photoshop locks up sometimes and hid all my layers. After I hid the layer I was working on I was able to save and exit. When I re-opened the project I was able to work normally.